In aqueous suspensions of powdery inorganic or organic substances such as hydraulic binders (e.g. cement, lime, gypsum plaster or anhydrite), rock flour, ground silicate, chalk, clays, porcelain slip, talc, pigments, carbon black or polymer powders, admixtures in the form of dispersants are often added to improve their processibility, i.e. kneadability, flowability, sprayability, paintability or pumpability. These admixtures are able to break up agglomerates and disperse the particles formed as a result of adsorption on the surface of the particles. This leads, particularly in the case of highly concentrated dispersions, to a significant improvement in the processibility.
Conventional cement dispersants or plasticizers which have hitherto mainly been used are salts of naphthalenesulphonic acid-formaldehyde condensates (cf. EP-A 214 412, hereinafter referred to as naphthalenesulphonates), salts of melaminesulphonic acid-formaldehyde condensates (cf. DE 16 71 017) and salts of polycarboxylic acids (cf. U.S. Pat. No. 5,707,445 B1, EP 1 110 981 A2, EP 1 142 847 A2).
As a substitute of the conventional dispersants, US 2008/0108732A1 discloses a polycondensation product consisting of component (A) an aromatic or heteroaromatic compound having 5 to 10 carbon atoms of which some are replaced by heteroatoms in case of heteroaromatic compound, the compound having at least one oxyethylene or oxypropylene group attaching the aromatic or heteroaromatic compound via an O or N atom, optional component (B) at least an aromatic compound selected from phenols, phenol ethers, naphthols, naphthol ethers, anilines, furfuryl alcohols and/or an aminoplast former selected from melamine (derivatives), urea (derivatives) and carboxamides, and component (C) an aldehyde compound selected from the group consisting of formaldehyde, glyoxylic acid and benzaldehyde and mixtures thereof. In some particular embodiments, the polycondensation product contains phosphate moiety.
The polycondensation product is produced by polycondensing components (A) and (C) and optional (B) in aqueous solution in the presence of a protonation catalyst. The catalyst used therein may be inorganic acids such as sulfuric acid.
The process according to US 2008/0108732A1 is disadvantageous in certain aspects. In this process, the aldehyde component (C) is preferably used in the form of aqueous solution, such as formalin. The aqueous solution introduces large amounts of water into the polycondensation system, which lowers down the catalyst concentration, for example, sulfuric acid concentration in the system on the one hand, and demands more energy to keep a suitable reaction temperature, for example 105-110° C., of the system on the other hand. As a consequence, long polymerization time such as 5 hours at 105-110° C. was generally needed to obtain a polymer with a practical molecular weight, e.g. Mn in the range of 18000 to 35000 g/mol, which means the efficiency of polycondensation is not satisfying. In commercial scale, the large amounts of water introduced with the aldehyde components (C) and the long residence time of the reaction materials result in the need of apparatus with large volume. The cost increases accordingly. Besides, during a long time of polycondensation, a loss of formaldehyde in case of a non-pressurized reactor due to its low boiling point (−21° C.) and a partial decomposition of product at high reaction temperature are unavoidable.
A process for producing phosphorylated polycondensation product is disclosed in WO 2010/040611A1, wherein at least one sulfonic acid is used as catalyst instead of sulfuric acid. As described therein, the obtained phosphorylated polycondensation product may be used as an additive for aqueous suspension of hydraulic and/or latent hydraulic binders. A phosphorylated polycondensation product is also disclosed in WO2010/040612A1, which may be used as flow promoter for hydraulic binders.
In the process according to WO 2010/040611A1, no insoluble salt of a catalyst is generated, which makes the process more economical in terms of the work-up procedure. However, it is well known that the cost of sulfonic acid is much higher than that of sulfuric acid.
Both of the processes according to US 2008/0108732A1 and WO 2010/040611A1 are disadvantageous in that the polycondensation period is relatively long. Generally, a period of 5 hours was needed to obtain a polycondensation product with a practical molecular weight, for example, Mn in the range of 18000 to 35000 g/mol.
It was therefore an object of the present invention to provide a process for producing a polycondensation product as dispersant for inorganic binders, with improved polycondensation efficiency.